1. Field
The invention lies in the field of orienteering, positioning and surveying instruments in general. More specifically, it refers to compass structure that allows a specific compass bearing to be identified with great accuracy, even for one with poor eyesight. More specifically the invention features a small handheld self-contained compass structure having a distant object viewing system and a compass face indicia viewing system, wherein the lines of sight of the two systems (lens sets) are in general alignment and wherein the focal points (on the viewers eye) for both systems are substantially coextensive, and whereby extremely rapid eye sighting from one line of sight to the other will not require any significant physiological change in the users eye lens.
2. Prior Art
There is considerable prior art in the area of sighting compasses, navigational instruments or peloris, and optical viewing instruments. There are commonly found small handheld instruments with open sights and mirrors to allow the compass bearing readings to be viewed. There are existing instruments that allow a magnified viewing of the compass bearing readings. However, these prior instruments lack accuracy because it is not possible to see the bearing information, both far and close, practically simultaneously without moving the head or unit and thus the body, and without refocusing of the viewers eye lens.
Also, there are more complicated units such as in U.S. Pat. No. 2,970,510 that magnify the compass bearing readings and insert them into the field of view of the far target. These instruments are complicated to construct and/or they block the viewing of the far target. Since it is essential that any magnetic disk type compass be held at a level position, having a part of the distance viewing blocked and not being able to tilt the compass to compensate can make it unusable in a field situation. Also, no teaching of creating a collaborative pair of sighting systems having the same focal point as in the present invention is present in any of the prior art.
There is not an instrument that both (a) leaves the field of view of the far target unobstructed, and (b) delivers to the observer corrected views of both the far and near target to the same focal plane or point, with magnification of the bearing readings for increased accuracy. Nor is there such an instrument that allow declination correction with accuracy and ease and an instrument with so few parts. Nor is there an instrument that can give accurate readings with such an ease of use and that can be as compactly constructed and at such a light weight for use by backpackers or others where weight is a big consideration.
Further, in conjunction with the present compass structure in a preferred embodiment with an object alignment mark on the separate, isolated far distance viewing system, and with magnification of the compass face viewing, it is possible to achieve an accuracy in measurement not available in any current handheld compass devices. One-half degree increments of markings of ⅛ inch in length and less and with similar spacings therebetween are easily discernable on an appropriate magnetic disk.